1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device that improves picture quality by reducing a feed-through voltage and signal interference.
2. Discussion of the Related Art
Generally, a liquid crystal display device controls a light transmittance of a liquid crystal by use of an electric field, thereby displaying a picture. The liquid crystal display device includes a liquid crystal display panel where liquid crystal cells are arranged in a matrix and a drive circuit to drive the liquid crystal display panel.
A liquid crystal display device of the related art, as shown in FIG. 1, includes data lines D1 to Dm and gate lines G1 to Gn which cross each other in a liquid crystal display panel 15; and a thin film transistor (hereinafter “TFT”) for driving a liquid crystal cell Clc at each crossing point thereof. Further, the liquid crystal display panel includes a storage capacitor Cst for sustaining a voltage of the liquid crystal cell Clc. The liquid crystal cell Clc has an arrangement of liquid crystal molecules that is changed by an electric field which is applied to the liquid crystal cell when a data voltage is applied to a pixel electrode 11 and a common voltage Vcom is applied to a common electrode 12, thereby controlling the amount of transmitted light.
FIG. 2 represents a scan pulse SCP supplied to a gate line G1 to Gn and a voltage Vlc charged in a liquid crystal cell Clc.
Referring to FIG. 2, the scan pulse SCP swings between a gate high voltage Vgh which is set to be a voltage for turning on a TFT, and a gate low voltage Vgl which is set to be a voltage for turning off the TFT. The liquid crystal cell Clc is charged with a data voltage Vdata supplied to the data line D1 to Dm and the charged voltage is sustained for a fixed time during a scanning period when the scan pulse SCP remains at the gate voltage. On the other hand, if the common voltage Vcom is not set to be an optimum voltage or does not remain at the optimum voltage and is shifted toward a positive or negative polarity by as much as an offset voltage Voffset of FIG. 2, a residual DC voltage as much as the offset voltage Voffset is applied to both ends of the liquid crystal cell Clc. As a result, the liquid crystal cell Clc is not charged with the data voltage Vdata corresponding to a video data, but is periodically charged with a voltage which increased by as much as the offset voltage Voffset and a voltage which is decreased by as much as the offset voltage Voffset. If the common voltage Vcom is not optimized, a flicker phenomenon where flickering is generated for each frame period appears in a screen or an afterimage appears in the screen. For example, when the liquid crystal display device is driven at 60 Hz, the screen flickers with a period of 30 Hz. Further, the related art liquid crystal display device is driven with drive circuits at one side, as shown in FIG. 1, except in a case of a large screen. If the liquid crystal display device is driven with drive circuits at one side, a signal 32 transmitted to a final pixel is distorted by a resistance and a capacitance within the liquid crystal display panel in comparison with a signal 31 inputted as in FIG. 3. A feed through voltage deviation ΔVp within the liquid crystal display panel generated in this way becomes a cause of the flicker generation, thus the flicker and the after image become worse as the feed through voltage is higher, thereby causing a picture quality defect as a result thereof.